Automatic container filling machines involve a series of beverage dispensing valves and conveyor mechanisms which automatically operate to bring the containers to be filled into contact with the valves and seated against the valves, whereupon the beverage is automatically discharged into the containers. The containers are usually glass bottles or metal cans. Particularly when filling containers for carbonated soft drinks, beer, and the like, it is necessary to provide a vent for the gas in the containers. For this reason the filler valve mechanisms are provided with vent tubes which permit the gaseous contents of the containers to flow out of the containers as the liquid flows in. A central vent tube is associated with each valve, and is automatically inserted into the container by the machine before the filling is commenced, the vent tube projecting downwardly into the container.
Since the machines operate at high speeds, it is essential that the flow of liquid into each container be shut off when the containers are accurately filled to a desired level. Each vent tube acts not only to vent the gas from the container but also to accuate a mechanism for shutting off the flow of beverage into the container when the beverage reaches the desired level.
An example of a typical container filling machine is disclosed in U.S. Pat. No. 3,179,133. As disclosed in this patent, the height to which the container is filled is determined by the level of a vent aperture in the wall of the vent tube. This aperture is placed at the level of the desired fill height in the container. When the liquid in the container reaches the level of the fill height, it prevents the flow of gas into the vent aperture and through the interior passage of the tube. An automatic mechanism in the valve shuts off the flow of liquid into the container when the flow of gas has been blocked. There are various known types of valve mechanisms for filling machines that operate in this manner, and the construction of the valve mechanism per se does not form a part of this invention.
The fill height varies in different filling operations depending upon the size and shape of the containers and other factors. It is, therefore, necessary to adjust the level of the aperture in the vent tube. Various constructions of vent tubes have been proposed in order to provide the necessary adjustable vent aperature. For example, U.S. Pat. No. 3,179,133 shows a vent tube having an axially extending slot in the wall of the tube, and a snugly fitting sleeve disposed on the exterior of the tube that may be adjusted along the tube so as to close off the slot or slots in the wall of the tube above the level of the desired fill height. Vent tubes having exterior sleeves of this type, however, have serious problems. These sleeves are subject to damage by engagement with the bottles or other containers as they are moved into position for filling by the machine. In modern high-speed filling machines, engagement with the container is a particularly serious problem because of the possibility, not only of damage to the sleeves, but also of displacing the sleeves on the exterior of the vent tubes so as to change the position of the vent aperture. To prevent the possible displacement of the sleeve, it has been the practice to provide very tightly fitting sleeves on the exterior of the vent tube, making adjustment of the sleeves very difficult. Adjustment of the tightly fitted sleeves also causes the material to be roughened; fragments may be dislodged from the sleeve and fall into the container. The roughened sleeve also may result in undesirable foaming of the liquid being filled into the container. Foaming is particularly undesirable because it results in inaccuracy in the amount of product placed in the container. Furthermore, the range of adjustment of the exterior sleeve is limited by the placement of the spreader on the exterior of the sleeve.
To remedy some of the problems associated with the adjustable vent tubes of the prior art, I have disclosed in my co-pending patent application Ser. No. 624,010, filed Oct. 20, 1975, a vent tube with an internal controlling member disposed within the tube for blocking the passage of the flow of gas into an elongated slot on the wall of the tube. While this construction overcomes many of the problems associated with the prior art vent tubes, it still requires a tedious adjustment of the vent aperture by vertically moving the controlling member for each different filling operation.
A two-piece vent tube having an upper member or body and a removable lower member or tip has also been proposed. To adjust the vent aperture and the fill height, the tube tip is removed and is replaced by another tip having an aperture at a different level. This construction allows for rapid adjustment of the fill height by removal of one tube tip and replacement by a different one. The construction of prior two-piece vent tubes, however, has created problems in their use. The tube tip generally fits over the bottom end of the vent tube body. This connection may be subject to failure because the tube tips are often fabricated of relatively soft plastic to prevent damage to the containers during the insertion of the vent tubes. The soft plastic material of the tip may swell when wet and it may stretch by repeated placements over the bottom end of the tube body, and eventually the connection between the tip and the body can become loosened and the tip may fall off into the container during the filling process, or permit leakage of the gas into the interior passage of the vent tube after the liquid has reached the level of the vent aperture, causing the container to overfill.
Another problem with the two-piece vent tubes of the prior art concerns the design of the locking mechanism between the two pieces. The removable tip must be firmly secured to the vent tube body to prevent leakage and to prevent the tip from loosening during the filling process when it is subject to high speed flows of beverage and venting gas. For the locking mechanism between the two pieces to be sufficiently secure, a great deal of effort is required to remove the tip when exchanging one tip for another with an aperture at a different fill height. In order to grip the tube tip, pliers or other tools are often used to remove the tip, but such tools can cause damage to the tips if used repeatedly. Another method of removal was to place a tool, such as an ice pick, through the lateral vent apertures to pull off the tube tip. This method, however, may also result in damage to the tip, causing inaccurate fill heights.